There are two types of Big Bangs. One is the Big Bang Theory where once there was nothing and then it exploded on its own (not hardly). The other is the big bang is one that actually happens. You get it from water hammer in your plumbing system and it is both annoying and can stress your plumbing system.
Since air is a vapor, it compresses. However, water does not. So the the air chamber allows the water a place to temporarily expand into and softens the blow of the water shock wave occurring when the faucet is turned off quickly.
Water Hammer is the acoustic by-product of hydraulic shock in the plumbing system. It is by far the loudest and most common plumbing noise problem in the home. You will hear it in a home having high water flow rates of about 10 feet / second and when a water valve or faucet is quickly shut off.
Older homes will usually have what is called an "air chamber" located on the hot and cold water lines. They will be located at or near each faucet or water inlet valve. The purpose of the air chamber is to act like a shock absorber for water when it is flowing under pressure and at high speed.
In situations when you need to drain your home's entire plumbing system, such as when you are winterizing it, you need to learn how to drain the system so that air can refill the air chamber.